From the mid-2000s, Sukhoi and its KnAAPO division further developed the Su-35 concept and improved it with additional cutting-edge technologies eyeing potential foreign sales, marketing it as Su-35BM (Bolshaya Modernizatsiya, or "Big Modernization"). The experiences of 2008 South Ossetia war has also opened its prospects to replace ageing Su-27 fighters in the Russian Air Force's fleet. The modernized Su-35 will serve as an interim design until the fifth generation Sukhoi PAK FA fighter enters service. The modernized Su-35 is considered to be 4++ generation by Sukhoi.
The modernized Su-35 was presented at the 2007 MAKS Airshow. The new features of the aircraft include a reinforced airframe with a more extensive use of titanium alloys, thus increasing the airframes durability to some 30 years or 6,000 service hours, a reduced radar signature from the front, and an improved passive electronically scanned array radar. It is now capable of supercruise. The aircraft featured many other upgrades to its avionics and electronic systems, including digital fly-by-wire and a rear-looking radar for firing semi-active radar homing missiles. The new Su-35 omits the canard andspeedbrake; to maintain manoeuvrability equal to or greater than canard-equipped fighters, the Su-35 uses the new 117S engine with fully rotating vectoring thrust nozzles.
The new Su-35 version first flew on 19 February 2008. On 14 April 2009, a Su-35BM prototype crashed during a high-speed ground test. The test pilot escaped unharmed. According to Sukhoi, the fighter's brakes failed during landing, resulting in the speeding aircraft going off the runway and the left engine catching fire. On 18 August of the same year, the Russian Defense Ministry announced a contract for 48 Su-35S (Serial) fighters along with 16 Su-27/30 fighters to be delivered by 2015. Sberbank agreed, in September 2010, to provide funding for the Su-35 program. In November 2009, Sukhoi started manufacturing on the first serial aircraft. On 14 October 2010, Sukhoi announced that the first production Su-35S had completed general assembly and that the first aircraft would be delivered to the Russian Ministry of Defense by the end of the year. In May 2011, the first production model Su-35S was flown for the first time. In 2009, Sukhoi estimated that the Su-35 would be manufactured at a rate of 24 to 30 aircraft each year from 2010 to 2020. By March 2012, four series Su-35S aircraft had been completed. Russia is to receive 48 Su-35S aircraft from 2011 to 2015.
On 4 April 2012, the Su-35 completed 500 test flights.